On 24 February 2022, Russian forces invaded Ukraine, intending to overthrow the Zelensky government and bring the former Soviet republic back into the Russian sphere of control. Vladimir Putin clearly expected a quick victory and many in the West also predicted that Kiev would fall in a few days. But they hadn’t counted on the skilled, courageous and determined resistance of the Ukrainian armed forces, nor the degree to which Russian military might had been overestimated. The initial Russian dash for Kiev was thrown back and their advances in the east and south also slowed by a combination of fierce resistance and their own unpreparedness, inadequate logistical planning and incompetent command. While the Russians ground their way forward in the east and south of the country, devastating towns and cities, they paid a heavy price in casualties and equipment losses. A carefully planned Ukrainian counteroffensive in the summer forced the invaders into a series of humiliating retreats. As winter approached, the Russians still held considerable territory but the initiative and strategic momentum had clearly swung to the defenders. The illusion of Russian invincibility was shattered forever. US Major General (retired) John S Harrel, a graduate of the US Army War College, trained with the Ukrainian army in the 1990s and in 2006, and commanded Ukrainian troops as part of the NATO force in Kosovo in 2005. His military expertise and detailed knowledge of the combatants informs this clear narrative and analysis of the course of the first 10 months of the war. He gives the reasons for the failure of the Russian invasion and, conversely, explains how the Ukrainian defence exceeded expectations, while acknowledging that strategic mistakes were made on both sides.